Patent Document 1 and Patent Document 2 disclose as a lock mechanism for when a seat back is stopped at a predetermined inclination angle, a technique using a slide member that contacts with a tooth surface of a worm and stops the rotation of the worm by friction, and a technique that moves the worm itself in parallel to a worm wheel and pushes the worm against the worm wheel to stop the rotation of the worm by friction. This structure requires a large pushing force in order to acquire necessary locking force.
Between teeth of the worm and worm wheel, backlash exists for smooth rotation movement. However, this backlash may be a factor generating looseness and abnormal sounds at the time of locking of the seat back.
However, for smooth rotation movement of the worm and the worm wheel, a size of the backlash must be adjusted on the basis of a certain engagement relationship by strictly aligning a bearing that pivotally supports both end portions in an axial direction of the worm. Since the backlash is changed by manufacturing errors of the worm or the like, abrasion and deformation of the teeth used, or the like, reducing variation for every product is difficult. Even when, at the time of locking, the worm is pushed against the worm wheel, a clearance is kept generated between teeth of the worm and the worm wheel along a thrust direction of the worm and the clearance may be a factor generating looseness and abnormal sounds at the time of locking.
On the other hand, the present applicant suggests following mechanisms in Patent Document 3 and Patent Document 4 as a mechanism capable of eliminating even the clearance in the thrust direction of the worm at the time of locking.
That is, Patent Document 3 suggests a reclining adjuster in which a worm formed with dent portions in both end surfaces is used, a bearing including a dent portion in an opposite surface with the worm is fixed in a bracket, and a support mechanism of the worm loaded with a ball between the worm and the bearing is adopted. When the reclining adjuster stops a seat back at a predetermined inclination angle, teeth portion of the other end side in an axial direction of the worm is pushed against a worm wheel by a pushing means and is locked. Patent Document 4 suggests a mechanism in which, in order to make a movable range of the worm larger than the technique of Patent Document 3, a movable bearing that moves vertically is provided in the other end side in an axial direction and the movable bearing is moved vertically and is pushed against the worm wheel.